Midkine (hereinafter, referred to as “MK”) is a growth/differentiation factor found as a product of a gene transiently expressed in the stage of retinoic acid-induced differentiation of embryonal carcinoma (EC) cells and is a polypeptide of 13 kDa in molecular weight rich in basic amino acids and cysteine (Kadomatsu. et al. (1988) Biochem. Biophys. Res. Commun., 1511312-1318; Tomokura et al. (1999) J. Biol. Chem., 265:10765-10770).
MK is known to have various biological activities. For example, it is known that MK expression is increased in human cancer cells. This increase in expression has been confirmed in various cancers such as esophageal cancer, thyroid cancer, urinary bladder cancer, colon cancer, stomach cancer, pancreatic cancer, thoracic cancer, liver cancer, lung cancer, breast cancer, neuroblastoma, glioblastoma, uterine cancer, ovarian cancer, and Wilms tumor (Muramatsu (2002) J. Biochem. 132:359-371). Moreover, MK is thought to promote the survival and migration of cancer cells, promote angiogenesis, and contribute to cancer progression.
MK is also known to play a central role in the stage of inflammation formation. For example, it is known that neointimal formation after vascular injury and nephritis onset during ischemic injury are suppressed in knockout mice deficient in MK genes. Moreover, it is also known that rheumatism models and postoperative adhesion are significantly suppressed in such knockout mice (WO2000/10608; WO2004/078210). Thus, MK is known to participate in inflammatory diseases such as arthritis, autoimmune disease, rheumatic arthritis (rheumatoid arthritis (RA) or osteoarthritis (OA)), multiple sclerosis, postoperative adhesion, inflammatory bowel disease, psoriasis, lupus, asthma, and neutrophil dysfunction. Furthermore, MK is known to promote the movement (migration) of inflammatory cells such as macrophages or neutrophils. Since this movement is necessary for the establishment of inflammation, it is thought that deficiency of MK probably prevents diseases based on inflammation (WO1999/03493).
The three-dimensional structure of MK has been determined by NMR and reported (Iwasaki et al. (1997) EMBO J. 16, p. 6936-6946). MK is composed of: an N-terminal fragment (hereinafter, referred to as an “N-fragment”) consisting of amino acid residues 1 to 52; a C-terminal fragment (hereinafter, referred to as a “C-fragment”) consisting of amino acid residues 62 to 121; and a loop region (amino acid residues 53 to 61) (hereinafter, referred to as a “loop”) that links these fragments. Each of the N- and C-fragments is mainly composed of: a portion having a three-dimensional structure consisting of three antiparallel [beta]-sheets (hereinafter, referred to as a “domain”; the domain (consisting of amino acid residues 15 to 52) in the N-fragment is referred to as an “N-domain”, and the domain (consisting of amino acid residues 62 to 104) in the C-fragment is referred to as a “C-domain”); and a terminally located portion devoid of the domain that does not assume a particular three-dimensional structure (hereinafter, referred to as a “tail”; the tail (consisting of amino acid residues 1 to 14) in the N-fragment is referred to as an “N-tail”, and the tail (consisting of amino acid residues 105 to 121) in the C-fragment is referred to as a “C-tail”). Basic amino acids on the C-domain surface form two clusters: a cluster consisting of lysine 79, arginine 81, and lysine 102 (cluster I) and a cluster consisting of lysine 86, lysine 87, and arginine 89 (cluster II). Both the clusters are known to participate in heparin-binding ability.
The C-terminally located domain is usually responsible for MK activity (Kojima et al. (1995) Biochem Biophys. Res. Comm. 206:468-473; Muramatsu et al. (1994) Biochem Biophys. Res. Comm. 203:1131-1139; Matsui et al. (2010) Int. Arch Medicine 3:12). Development of anti-MK antibodies has therefore focused on antibodies which are directed against the C-domain.